Antimicrobial Efficacy of External Fixator Pins Coated

Antimicrobial Efficacy of External Fixator Pins Coated with aLipid Stabilized Hydroxyapatite/Chlorhexidine Complex toPrevent Pin Tract Infection in a Goat ModelMAJ E. Schuyler DeJong, MD, MAJ Thomas M. DeBerardino, MD, Daniel E. Brooks, BS,MAJ Bradley J. Nelson, MD, Allison A. Campbell, PhD, MAJ Craig R. Bottoni, MD, Anthony E. Pusateri, PhD,MAJ Ronald S. Walton, DVM, MS, Charles H. Guymon, MA, and Albert T. McManus, PhD

Background: Pin tract infection is acommon complication of external fixation.An antiinfective external fixator pin mighthelp to reduce the incidence of pin tractinfection and improve pin fixation.

Methods: Stainless steel and titaniumexternal fixator pins, with and without alipid stabilized hydroxyapatite/chlorhexi-dine coating, were evaluated in a goatmodel. Two pins contaminated with an

identifiable Staphylococcus aureusstrainwere inserted into each tibia of 12 goats. Thepin sites were examined daily. On day 14,the animals were killed, and the pin tipscultured. Insertion and extraction torqueswere measured.

Results: Infection developed in 100%of uncoated pins, whereas coated pinsdemonstrated 4.2% infected, 12.5% colo-nized, and the remainder, 83.3%, had no

growth (p < 0.01). Pin coating decreasedthe percent loss of fixation torque overuncoated pins (p 5 0.04).

Conclusion: These results demon-strate that the lipid stabilized hydroxyap-atite/chlorhexidine coating was successfulin decreasing infection and improving fix-ation of external fixator pins.

Key Words: External fixation, Pin,Infection, Hydroxyapatite, Chlorhexidine.

J Trauma.2001;50:1008–1014.

Pin tract infection is an unfortunate but common com-plication of external fixation. Rates of pin tract infec-tion vary widely in the literature. Major pin tract infec-

tion, defined as requiring hospital admission for parenteralantibiotic therapy, pin removal, or fixator removal, averages5.8%.1 Overall rates of pin tract infection, to include lesssevere infections, have been reported as high as 100%.1 It isunclear whether loosening and separation precede or followthe onset of pin sepsis. In either case, however, infected pinsites are associated with pin loosening, fracture destabiliza-tion, and osteomyelitis.2

An additional problem arising from pin tract infection isthe risk of infection when converting external fixation tointernal fixation. The incidence of deep infection after theconversion of external fixation to intramedullary nailing ofthe tibia has been reported at up to 71% when performed afterthere has been evidence of a pin site infection.3,4 This is in

contrast to a 5.9% deep infection rate when converting ex-ternal fixation to intramedullary nailing in the absence of pinsite infection.3 Additional studies support low rates of deepinfection, from 0% to 5.9%, resulting from intramedullarynailing after external fixation when pin tract infection wasabsent or adequately treated.5–7

In an effort to decrease pin tract infection while main-taining pin stability, a unique pin coating was conceived anddeveloped in a cooperative research agreement. This coatingcombines hydroxyapatite, with its ability to improve the in-terface between bone and metal implants, and chlorhexidine,with its low toxicity and broad antimicrobial activity.8 Thisprocess has been refined to increase the amount of chlorhexi-dine applied to the pin, and incorporates a lipid coating toslow the elution of the chlorhexidine. The purpose of thestudy was to evaluate the ability of this lipid stabilized hy-droxyapatite/chlorhexidine coating to reduce the incidence ofpin tract infection and improve pin fixation in a goat model.

MATERIALS AND METHODSPin Coating

The pin coating is applied through a multiple layeringprocess of hydroxyapatite and chlorhexidine. A surface-in-duced mineralization technique was used to produce a hy-droxyapatite coating on the external fixator pins. Chlorhexi-dine was then incorporated into the coating by placing thehydroxyapatite-coated pin into a chlorhexidine solution.8

This process of hydroxyapatite mineralization followed bychlorhexidine addition was repeated at least four times untilthe coating was of the desired thickness (6–10mm). To slowthe release of the chlorhexidine from the coating, a lipid

Submitted for publication October 28, 2000.Accepted for publication February 22, 2001.Copyright © 2001 by Lippincott Williams & Wilkins, Inc.From the Extremity Trauma Study Branch (E.S.D., D.E.B., A.E.P.,

R.S.W.) and Microbiology Division (C.H.G.), U.S. Army Institute of Sur-gical Research (A.T.M.), and Orthopaedic Surgery Service (T.M.D.), BrookeArmy Medical Center, Fort Sam Houston, Texas, Orthopaedic SurgeryService (B.J.N.), Eisenhower Army Medical Center, Fort Gordon, Georgia,Material Sciences Department (A.A.C.), Battelle, Pacific Northwest NationalLaboratories, Richland, Washington, and Orthopaedic Surgery Service(C.R.B.), Tripler Army Medical Center, Honolulu, Hawaii.

Presented at the 60th Annual Meeting of the American Association forthe Surgery of Trauma, October 11–15, 2000, San Antonio, Texas.

Address for reprints: MAJ E. Schuyler DeJong, MD, OrthopaedicSurgery Service, Brooke Army Medical Center, 3851 Roger Brooke Drive,Fort Sam Houston, TX 78234-6200.

The Journal of TRAUMAt Injury, Infection, and Critical Care

1008 June 2001

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4. TITLE AND SUBTITLE Antimicrobial efficacy of external fixator pins coated with a lipidstabilized hydroxyapatite/chlorhexidine complex to prevent pin tractinfection in a goat model

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6. AUTHOR(S) DeJong, E. S. DeBerardino, T. M. Brooks, D. E. Nelson, B. J. Campbell,A. A. Bottoni, C. R. Pusateri, A. E. Walton, R. S. Guymon, C. H.McManus, A. T.

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overlayer was applied to the coated pins. The lipid creates abiocompatible layer over the coating that slowly dissolves,slowing the release of the chlorhexidine.

The pin coating was evaluated using scanning electronmicroscopy to ensure the durability of the hydroxyapatitecoating both after the addition of chlorhexidine and afterrelease of the chlorhexidine in a saline bath. Figure 1A showsa typical appearance of the coating with chlorhexidine incor-porated. There were no indications that the incorporation ofchlorhexidine causes the dissolution of the hydroxyapatitecoating or alteration of the phase of the mineral deposited.Figure 1B shows the coating after soaking in a saline bath for48 hours. The coating exhibits only a small fraction of dis-solution demonstrated by the roughened edges of the hy-droxyapatite crystals. It is important that the release of thechlorhexidine not be because of the complete dissolution ofthe hydroxyapatite coating, since the hydroxyapatite en-hances pin fixation.

Experimental MethodsThe experimental protocol used for this work was eval-

uated and approved by the Institutional Review Board and theInstitutional Animal Care and Use Committee. Animals wereobtained from a single licensed vendor and maintained in asecure, climate-controlled facility for the duration of theexperimental protocol. Adherence to established guidelinesfor the treatment of animal subjects was strictly maintained.

Twelve mature castrated male Spanish goats were usedfor this study. Veterinary staff evaluated the animals initiallyand observed them for 1 week to exclude the possibility ofpreexisting disease or untreated parasitic condition. The an-imals were fasted for 48 hours before surgery. Preoperatively,the animals were sedated, then anesthetized with generalendotracheal anesthesia. Epidural morphine sulfate (Du-ramorph, 0.1 mg/kg) was administered via spinal needle as anepidural analgesic for perioperative and postoperative painmanagement.

The hindlimbs of each animal were prepared using achlorhexidine scrub. Incisions 2.5 cm in length were made inthe medial aspect of both hindlimbs, the first placed 3 cmabove the ankle joint and the second placed 10 cm above thefirst. The incisions were made on the subcutaneous border ofthe tibia. Hemostasis was maintained with electrocautery.The periosteum was incised and retracted. The proper 3.0/4.0-mm external fixator pin (Synthes, Monument, CO) wasinserted into the medial tibial face with the use of a powerdrill. Each animal received one of each of the followingexternal fixator pins (Fig. 2): an uncoated stainless steel pin,an uncoated titanium pin, a lipid stabilized hydroxyapatite/

Fig. 1. (A) Scanning electron micrograph of hydroxyapatite coat-ing after the incorporation of chlorhexidine. (B) Scanning electronmicroscopic image of hydroxyapatite/chlorhexidine coating aftersoaking for 48 hours in saline solution.

Fig. 2. External fixator pins from left to right: uncoated stainlesssteel, uncoated titanium, coated stainless steel, and coated titanium.

Evaluation of Antimicrobial External Fixator Pins

Volume 50 • Number 6 1009

chlorhexidine coated stainless steel pin, or a lipid stabilizedhydroxyapatite/chlorhexidine coated titanium pin.

The assignment of pin type to pin site was balanced sothat each pin type was represented equally at each pin sitelocation. Each pin was inoculated with 30mL of a 106 colonyforming units (CFU)/mL solution ofStaphylococcus aureus(ATCC 29213), applied to the pin threads, before final inser-tion. This bacterium has been genetically selected to be re-sistant to streptomycin to facilitate bacterial identification.The pin insertion was completed by hand so as to confirmadequate placement through the far cortex of the tibia. Torquemeasurements were taken with final insertion (BGI RemoteSensor, STE200 torque wrench extension, Mark-10 Corpora-tion, Hicksville, NY) by the first author (E.S.D.) in all mea-surements. After placement of the pins, the wounds were leftopen and sterilely dressed with pin dressing sponges (Smith& Nephew, Inc., Memphis, TN) and sponge clips. The pinswere cut short, approximately 2 cm above the sponge, and pincaps were applied to the cut pin ends. Gauze roll and astockinette were then applied. Each goat was then extubatedand allowed to recover in its cage under the direct supervisionof a veterinarian technician.

Daily evaluations of each pin site by three independentobservers began after an initial incubation period of 48 hoursafter surgery. The dressings were carefully changed to avoidcross-contamination of the pin sites. The condition of the pinwas annotated individually by each observer as one of thefollowing: no infection, inflammation or serous drainagewithout frank purulence, or frank purulence at the pin site.The clinical determination of infection was defined as allthree observers agreeing that purulent drainage was present ata given pin site on any one day during the clinical evaluationperiod. After evaluation, the pins were superficially wipedclean with a dry sterile gauze, new pin dressing sponges wereapplied to the pin sites, the pin sites were overwrapped toavoid cross-contamination, and the animals were returned totheir individual pens.

On postoperative day 14, the animals were killed. Eachpin site was assessed for purulent drainage and scored ac-cording to the criteria listed above. Next, the soft tissue wascarefully stripped from around each pin in preparation for pinremoval. Extraction torque was measured for each pin by thefirst author. Each pin was then removed, and the terminal 10mm of the pins were sterilely cut and placed into phosphate-buffered saline with 0.01% trypsin. The pin tips were vor-texed for 30 seconds, then sonicated for 3 minutes to removethe bacteria from the tip. Quantitative bacterial counts wereperformed by the spread plate method on trypticase soy agar.9

Isolation and identification of the bacterial species was per-formed on MacConkey agar plates and trypticase soy agarplates with 5% sheep blood. Isolates were identified by rou-tine mirobiologic procedures. EachS. aureusisolate wastested for streptomycin resistance to assess if it was the samestreptomycin-resistant strain as that from the initial pininoculation.

Data AnalysisTorque data were analyzed by analysis of variance. CFU

data were analyzed by Mann-WhitneyU test. Means6 SEMare reported for torque data. Discrete data, such as trueinfection rate, were analyzed byx2. Statistical significancewas determined byp , 0.05. All data were analyzed usingSAS statistical software (SAS Institute, Cary, NC, 1989).

RESULTSEvaluation of the quantitative culture results from the

10-mm tip of the pins revealed that the uncoated pins devel-oped infection from the test strain in all 24 pins (100%), withan average total colony count from the pin tip of 3.23 106

(8.53 104 to 9.13 106) CFU (CFU per milliliter pin isolatesolution multiplied by volume of solution). The coated pinsdemonstrated no growth in 20 of 24 pins (83.3%), coloniza-tion in 3 of 24 pins (12.5%) with average total colony countsof 2,500 CFU (1,500–3,500) per pin tip, and infection in onepin (4.2%), demonstrating 3.33 104 CFU (Fig. 3). Thisdifference in infection rates between coated and uncoatedpins was significant (p , 0.001). No effect of metal type orpin location was found in evaluating culture results.

Clinical evaluations revealed purulence around 23 of 24uncoated pins (95.8%), whereas only 5 of 24 coated pins(20.8%) developed purulence (p , 0.01) (Fig. 4). No differ-ence in rates of pin purulence between metals was found.Combining clinical and microbiologic data, criteria for “con-firmed infection” were established. These criteria state that adiagnosis of “confirmed infection” requires both the appear-ance of clinical infection and positive microbiologic culturewith colony counts of 104 CFU/pin tip or greater. Using thesecriteria, the uncoated pins developed confirmed infectionfrom the test strain in 95.8% (23 of 24) of the cases, whereasthe coated pins had no infections (p , 0.01) (Fig. 4).

Evaluating pin fixation torque data, it was found that allpins had a reduction in fixation torque from insertion toextraction. However, combining metals, pin coating de-creased the percent loss of fixation torque compared with

Fig. 3. Percent infection by pin tip culture.


1010 June 2001

uncoated pins (p 5 0.04) (Table 1). Furthermore, titaniumpins were found to retain fixation strength better than stain-less steel pins (p , 0.01).

DISCUSSIONDifferent methods have been used to improve the inter-

face between external fixator pins and bone. Titanium coatingof stainless steel pins was shown to result in greater extrac-tion torques than uncoated stainless steel pins, after implan-tation in a sheep model for 6 weeks.10 Other studies haveshown that hydroxyapatite improves the bone-pin interfacewhen coated onto external fixator pins.10–15 Hydroxyapatitecoating has resulted in improved fixation of external fixatorpins in both animal models and human clinical trials. In onehuman clinical study, hydroxyapatite-coated and uncoatedstainless steel pins were compared. The authors found im-proved removal torque and a decreased incidence of pin tractinfection in the hydroxyapatite-coated pins, leading the au-thors to conclude that improved pin stability was responsiblefor the decrease in pin tract infection.12

In addition to improving stability of external fixator pins,our goal was to develop a pin that would actively resistinfection. Hydroxyapatite ceramics have been used as a de-livery system for antibiotics.16,17 A hydroxyapatite-coatedpin could thus potentially improve fixation and deliver ananti-infective compound to actively resist infection. Anti-infective techniques for external fixator pins used in the pastinclude the use of tobramycin-impregnated sleeves that fitover pins. These were tested in a goat model, and effectivelyeliminated induced infection.18 However, the environment ofan external fixator pin exposes the pin constantly to bacterialpathogens. Using an antibiotic, under such circumstances,might lead to resistant pathogens, defeating the pin’s purposeand possibly creating more resistant, difficult-to-treatorganisms.19

A disinfectant, with a lower chance of resistance devel-opment than an antibiotic, may be a better solution to reduc-ing pin tract infection. Silver-coating of external fixator pinsto decrease pin tract infection has been used in the past;however, studies demonstrate little20 or no improvement21 in

Fig. 4. Pin listing by pin type with clinical microbiologic (14 days after insertion), and combined infection data listed. “Clinical” refers topurulent drainage at pin site during daily dressing changes. “Confirmed Infection” requires clinical purulence and positive microbiologiccultures.Light shadingindicates colonized,dark shadingindicates infection.

Table 1 Insertion and Removal Torque Presented as Mean6 SE

UncoatedStainless Steel

Coated StainlessSteel

UncoatedTitanium Coated Titanium

Insertion torque (in-lb) 18.0 6 1.2 16.0 6 1.2 13.6 6 1.2 15.9 6 1.2Removal torque (in-lb) 8.4 6 0.8 9.1 6 0.8 8.6 6 0.8 10.4 6 0.8Change in torque (in-lb) –9.6 6 0.6a –6.9 6 0.6a –5.0 6 0.6a –5.5 6 0.6a

Percent change in torque –54.8 6 2.8a,b –44.6 6 2.8a,b –35.8 6 2.8a,b –34.0 6 2.8a,b

a Titanium pins had decreased loss of fixation torque and decreased percent change of fixation torque vs. stainless steel pins (p , 0.01).b Coated pins had decreased percent change of fixation torque vs. uncoated pins (p 5 0.04).



infection rates over uncoated stainless steel pins. Chlorhexi-dine is a commonly used disinfectant for hand washing andsite preparation for surgical procedures. This disinfectantprovides a high level of antibacterial activity with low levelsof resistance.19,22–24 Concentrations of chlorhexidine re-quired for bacterial inhibition are low, with concentrations of10 to 50 mg/mL required for inhibition of most bacterialspecies.22,24Furthermore, low levels of bacterial resistance tochlorhexidine are maintained, even during prolonged use.19,23

Its mechanism of action combines the rapid bactericidal ac-tion of iodophors (which lack persistence) with the persistentaction of hexachlorophene.22

Chlorhexidine has been found to have low toxicity. Ex-tensive testing has been performed with both topical appli-cation of chlorhexidine over prolonged periods22 and internaluse of chlorhexidine, to include chlorhexidine-coated intra-venous catheters,19 chlorhexidine-impregnated surgicalmesh,25 and chlorhexidine-containing irrigation for chronicperitoneal dialysis,26 without significant toxicity. As a resultof this low level of toxicity, chlorhexidine has Food and DrugAdministration approval for human use when applied to in-ternally placed medical devices, to include intravenous cath-eters and implanted antimicrobial surgical mesh.27

In this study, we demonstrated that with bacterial con-tamination of external fixator pins, infection from the inoc-ulated strain of bacteria, as demonstrated by microbiologiccultures, developed in all uncoated pins. This demonstratesthat in the absence of treatment, the experimentally inducedinfection will develop. In contrast, the hydroxyapatite/chlo-rhexidine coating reduced the rate of infection and the sever-ity of the infection in those pins that developed infection (p ,0.001). This suggests that the hydroxyapatite/chlorhexidinecoating was highly effective in reducing the incidence andseverity of pin tract infection in this experimental model.

Our method of external fixator pin contamination, adirect inoculation of the pin with bacteria during insertion,does not mirror how an external fixation pin would be in-fected clinically. However, our model does offer a reproduc-ible bacterial inoculum to the pin, allowing a highly repro-ducible pin tract infection in untreated pins. In anexperimental model, a highly reproducible pin tract infectionis desirable, as it allows for the evaluation of anti-infectivetreatments with a minimum number of animals. Without thisinoculation of bacteria to the pins, the degree of contamina-tion of each pin would be left to chance, substantially in-creasing the variability in the development of pin tract infec-tion, thus greatly increasing the number of animals needed toevaluate an anti-infective pin treatment.

During the daily pin evaluations, we noted that a fewcoated external fixator pins developed a clinical infection byour criteria, yet the pin tips were sterile at the termination ofthe study period (Fig. 4). We hypothesize that this is the resultof our establishing a soft tissue infection around the pin,which subsequently cleared, leaving the pin itself sterile.During insertion of the pin, a generous incision of approxi-

mately 2.5 cm was made. This was done to avoid tenting ortethering of the skin on the animal’s leg, which occurs duringflexion and extension of the limb as a result of the highmobility of the goat’s skin in this area. During application oftheS. aureusto the pin, which was performed when each pinwas partially inserted, a portion of the inoculum ofS. aureusmay have run into the soft tissues around the pin. In thisrelatively large wound, it appears from our daily observationsthat we established a soft tissue infection at the pin site of thecoated pins in some of the animals. Despite establishing thisperipheral soft tissue infection, which would have certainlyresulted in a constant exposure of the pin to the inoculatedbacteria over a prolonged period, the coated pins themselvesremained uninfected in the vast majority of cases. Thus, thepins were able to resist infection in the bone-pin interface notonly from the initial contamination of the pin withS. aureus,but also from a prolonged exposure to an infective organism.

Evaluation of our pin fixation torque data revealed thatall pins had a reduction in fixation torque from insertion toextraction. When comparing groups of pins, however, pincoating was noted to decrease the percent loss of fixationtorque as compared with uncoated pins. Furthermore, tita-nium pins, when considered together, were found to retainfixation strength better than stainless steel pins. These find-ings are congruent with other studies, which suggest that bothtitanium coating10 and hydroxyapatite coating10–15 can im-prove fixation as compared with uncoated stainless steel pins.The duration of our experimental protocol is fairly short,however, and prolonged implantation may be necessary tofully delineate differences in fixation torque of these pin andpin coating combinations.

CONCLUSIONIn conclusion, we found that the lipid stabilized hydroxy-

apatite/chlorhexidine coating was successful in decreasingthe incidence of pin tract infection as compared with un-coated pins in our in vivo goat model. The coated pinsdemonstrated a decreased percent loss of fixation torque ascompared with uncoated pins. Finally, titanium pins werefound to retain fixation strength better than stainless steelpins.

REFERENCES1. Green SA. Complications of external skeletal fixation.Clin Orthop.

1983;180:109–116.2. Green SA, Ripley MJ. Chronic osteomyelitis in pin tracks.J Bone

Joint Surg Am. 1994;66:1092–1098.3. Maurer DJ, Merkow RL, Gustilo RB. Infection after intramedullary

nailing of severe open tibial fractures initially treated with externalfixation. J Bone Joint Surg Am.1989;71:835–838.

4. McGraw JM, Lim EVA. Treatment of open tibial-shaft fractures,external fixation and secondary intramedullary nailing.J Bone JointSurg Am.1988;70:900–911.

5. Johnson EE, Simpson LA, Helfet DL. Delayed intramedullarynailing after failed external fixation of the tibia.Clin Orthop.1990;253:251–257.


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6. Blachut PA, Meek RN, O’Brien PJ. External fixation and delayedintramedullary nailing of open fractures of the tibial shaft.J BoneJoint Surg Am.1990;72:729–735.

7. Antich-Adrover P, Marti-Garin D, Murias-Alvarez J, Puenti-AlonsoC. External fixation and secondary intramedullary nailing of opentibial fractures.J Bone Joint Surg Br.1997;79:433–437.

8. Campbell AA, Song L, Li XS, et al. Development, characterization,and antimicrobial efficacy of hydroxyapatite-chlorhexidine coatingsproduced by surface-induced mineralization.J Biomed Mater Res.2000;53:400–407.

9. Chuard C, Vaudaux P, Waldvogel FA, Lew DP. Susceptibility ofStaphylococcus aureus growing on fibronectin-coated surfaces tobactericidal antibiotics.Antimicrob Agents Chemother.1993;37:625–632.

10. Moroni A, Toksvig-Larsen S, Maltarello M, et al. A comparison ofhydroxyapatite-coated, titanium-coated, and uncoated taperedexternal-fixation pins. An in vivo study in sheep.J Bone Joint SurgAm.1998;80:547–554.

11. Magyar G, Toksvig-Larsen S, Moroni A. Hydroxyapatite coating ofthreaded pins enhances fixation.J Bone Joint Surg Br.1997;79:487–489.

12. Moroni A, Aspenberg P, Toksvig-Larsen S, Falzarano G, Giannini S.Enhanced fixation with hydroxyapatite coated pins.Clin Orthop.1998;346:171–177.

13. Augat P, Hanselmann KF, Suger G, Fleishmann W. Increase ofstability in external fracture fixation by hydroxyapatite-coated bonescrews.J Appl Biomater.1995;6:99–104.

14. Caja VL, Moroni A. Hydroxyapatite coated external fixation pins, anexperimental study.Clin Orthop.1996;325:269–275.

15. Moroni A, Caja VL, Maltarello MC, et al. Biomechanical, scanningelectron microscopy, and microhardness analyses of the bone-pininterface in hydroxyapatite coated versus uncoated pins.J OrthopTrauma.1997;11:154–161.

16. Itokazu M, Ohno T, Tanemori E, et al. Antibiotic-labeledhydroxyapatite blocks in the treatment of experimental osteomyelitisin rats.J Med Microbiol.1997;6:779–783.

17. Shinto Y, Uchida A, Korkusuz F, et al. Calcium hydroxyapatiteceramic used as a delivery system for antibiotics.J Bone Joint SurgBr. 1992;74:600–604.

18. Voos K, Rosenberg B, Fagrhi M, Seligson D. Use of a tobramycin-impregnated polymethylmethacrylate pin sleeve for the prevention ofpin-tract infection in goats.J Orthop Trauma.1999;13:98–101.

19. Maki DG, Stolz SM, Wheeler S, Mermel LA: Prevention of centralvenous catheter-related bloodstream infection by use of an antiseptic-impregnated catheter. A randomized, controlled trial.Ann InternMed. 1997;127:257–266.

20. Collinge CA, Goll G, Seligson D, Easley KJ. Pin tract infections;silver vs uncoated pins.Orthopaedics1994;17:445–448.

21. Nelson BJ, DeBerardino TM, Brooks DE, et al. The efficacy ofsteel, silver-coated, and chlorhexidine/chloroxylenol-coated externalfixator pins in preventing pin tract infections in a caprine model.Transactions of the 45th Annual Meeting, Orthopaedic ResearchSociety, February 1–4, 1999, Anaheim, California.

22. Gardner JF, Gray KG. Chlorhexidine. In: Block SS, ed:Disinfection,Sterilization and Preservation. 3rd ed. Philadelphia: Lea & Febiger;1983:251–270.

23. Aly R, Maibach HI. Effect of antimicrobial soap containingchlorhexidine on the microbial flora of skin.Appl EnvironMicrobiol. 1976;31:931–935.

24. Freney J, Husson MO, Gavini F, et al. Susceptibilities to antibioticsand antiseptics of new species of the family Enterobacteriaceae.Antimicrob Agents Chemother.1988;32:873–876.

25. Choe JM, Ogan K, Bennett S. Antibacterial mesh sling: aprospective outcome analysis.Urology. 2000;55:515–520.

26. Fabbri L, Grimaldi C, Zucchelli P. Peritonitis in CAPD; treatmentwith chlorhexidine.Dialysis Transplant.1982;1:483–484.

27. FDA Product Approvals and Related Actions. Available at: http://www.fda.gov; select “Other Recent Approvals” under “ProductApprovals”; on “FDA Product Approvals and Related Actions” page,select “Archives” under “Medical Devices”; on “Medical DeviceApprovals” page, select “Searchable Databases”; on “MedicalDevice Approvals Database” page, select “Search the 510(k)Database.” Accessed January 27, 2001.

DISCUSSIONDr. Bruce D. Browner (Hartford, Connecticut): Dr.

Maull, Dr. Shackford, members, and guests, thank you for theopportunity to discuss this article. Over the past decade,mandatory seat belt use, drunk-driving control, airbags, andimproved car design have reduced the number of complexopen fractures, the major arena for external fixation.

Reliance on this technique has been further deempha-sized by the growing use of locked unreamed intramedullarynailing and minimally invasive plating. Automobile-pedes-trian encounters and motorcycles, however, continue to pro-duce complex upper and lower extremity injuries that requireexternal fixation.

It is still used for extended periods in posttraumaticreconstruction and the treatment of chronic osteomyelitis. Asall patients know who have had the device on their limbs orpelvis, pin tract infection is an enemy. They fight a constantborder war living with discomfort and pain, cleaning their pinsites, and remain anxious over increases in swelling, redness,and drainage, which could signify a major invasion.

The orthopedist must be vigilant as well, following thepin tracts radiographically to detect periosteal new bone for-mation and lysis, which confirm an incursion of infectingorganisms into bone. A surgical strike is often necessary tocurette dead bone from the pin tract and replace prematurelyloosened pins. In a worst-case scenario, infection can con-taminate the fracture site, bone graft, or subsequent intramed-ullary nailing.

As an old warrior who has struggled through many ofthese battles, I would welcome a new defensive weapon. Forthis reason, I was intrigued with the device described by theseauthors: a hydroxyapatite-coated pin that can slowly releasechlorhexidine through a superficial stabilizing layer of lipid.In the experimental model used, these results are impressive.I have a number of concerns that would have to be addressedbefore I could recommend widespread adoption of this devicefor military and civilian use, and I’ll go over them.

In this study, the infecting organisms were introduced bydipping the pin tips in bacterial cultures before insertion. Inthe clinical setting, the infection generally begins in the softtissue pin tract wound, extending in a small percentage ofcases down into the bony pin tract.

In a subsequent study, it would be interesting to see theinfection-suppressing capability of these pins if the bacteriawere introduced into the overlying soft-tissue wound after pininsertion.



Pin loosening results from a variety of factors includingmechanical loading, the reaction of bone to different materi-als in the pin, and infection. Aseptic loosening of pins fromthe first two factors can set the stage for subsequent infection.

A more convincing analysis of the resistance of differentpins to mechanical loosening and infection could be accom-plished in a subsequent study that should use osteotomy ofthe goat’s tibia and a standardized blunt injury to the hind-limb instead of using the intact tibia as was done in this study.The osteotomy should be stabilized, then, by insertion of thesame type of pins, coated and uncoated, with the releasingcapability that could then be connected together by a standardexternal fixator.

The 2 weeks between when the pins are inserted andwhen the animals are killed should be extended to 6 to 8weeks to allow a more clinically relevant period of loadingand a greater opportunity for pin loosening that could thenlead to subsequent infection.

As the authors have noted, other investigators have re-ported reduced loosening rates and less pin infection withhydroxyapatite coating alone. For this reason, subsequentstudies should include a group of pins that have hydroxyap-atite coating alone without the chlorhexidine-releasingcapability.

The ability of chlorhexidine to eradicateS. aureusin thisstudy was quite impressive. Its broad-spectrum bactericidalcapability and low toxicity would make it a good substance toincorporate into external fixation pin tract dressings.

It would be interesting to see a separate study in whichthe bony pin tract infection rates and loosening were studiedafter overlying pin tract wounds were treated with and with-out chlorhexidine-containing dressings. Extensive studies onthe biocompatibility of chlorhexidine have convinced theFood and Drug Administration to make it available in thecoatings of catheters and surgical mesh. However, they maynot yet have addressed the possible adverse effects of thissubstance on bone formation.

After removal of external fixator pins, the pin hole is thesite of weakness in the bone. This is strengthened by theformation of new bone in the periphery of the pin hole.

Some of the animals in a subsequent study would have tobe kept alive for an additional 6 weeks after pin removal todetermine whether or not the restrengthening bone formationhad occurred in the pin holes after the use of hydroxyapatite-chlorhexidine releasing pins.

In closing, I would like to commend Dr. Brad Nelson andDr. Allison Campbell for the invention of this device andcongratulate Major DeJong and his coauthors for their excit-ing study.

I hope that they will regard my criticisms as constructiveand urge them to continue their studies in this important area.Thank you, again, for the privilege of discussing this study.

MAJ E. Schuyler DeJong (closing): Thank you verymuch for your comments. You brought up some very goodpoints for us to consider in the future.


1014 June 2001

Documents

Antimicrobial Efficacy of External Fixator Pins Coated